The present invention relates to systems for sensing or measuring one or more parameters of blood from a blood vessel of a patient. More particularly, this invention relates to assemblies and methods useful for sensing a parameter of blood in vivo involving a catheter and a sensor probe a portion of which is located in a lumen of the catheter.
Sensors and sensor probes are well known, for example, for use in determining the concentrations (meaning to include therein the partial pressures of gases) of blood analytes or constituents of interest. Typically of interest is the determination of the concentration of gases, such as oxygen and carbon dioxide, of hydrogen ions (pH), of other electrolytes, of glucose and the like in the blood. These provide useful parameters for assessment of certain physiological conditions of a mammal, for example, a human medical patient.
Such sensors and sensor probes can be made sufficiently small in size to be used directly in vivo in a patient. This contributes to monitoring the condition of the patient on a continuous basis as opposed to older known procedures which require the extraction of a blood sample for determination in a remote laboratory of the constituents of interest in the blood.
An example of a useful blood sensor involves an optical indicator, such as a fluorescence indicator, located in association with a matrix material, such as a polymeric matrix material, on the optical face or surface of an optical fiber. Typically, a matrix material containing a fluorescent dye is loaded onto the optical surface of an optical fiber. Interaction of the dye with the component of interest, that is the component to be sensed, is monitored using optical signals carried by the optical fibers.
Maxwell U.S. Pat. No. 4,830,013 discloses in vivo sensing of various blood parameters using a sensor probe which is adapted to be inserted through a catheter into the cardiovascular system of a patient. A sensor probe is provided and preferably includes a plurality of sensors, each of which includes a sensor element adapted for sensing a parameter of blood and for providing a signal in response thereto and elongated transmission means, for example, an optical fiber, for transmitting the signal from the sensor element proximally.
The above-noted Maxwell patent discloses that the sensor is placed between 0.005 inch and 0.125 inch proximal of the distal opening of the lumen. An anti-clotting solution is provided through the lumen of the catheter to the patient. The combination of this solution and blood in the lumen creates an interface zone including both blood and anti-clotting solution. This interface zone is moved over the sensor so that the sensor can be bathed in blood for a period of time sufficient to enable the sensor to provide a signal relating to the blood parameter of interest, and to allow the anti-clotting solution to be expelled from the distal opening of the lumen. Thus, the sensor is either exposed to substantially exclusively blood or to a combination of blood and anti-clotting solution in the interface zone.
A related system is disclosed in Maxwell et al U.S. Pat. No. 4,951,669 in which the sensors are located in the fitting proximal of the catheter. In one embodiment, the sensors are shown in the lumen near the enlarged proximal end of the catheter. This system, which can be operated very similarly to the system in the above-noted Maxwell patent, is designed to allow the use of bigger sensor elements. Both the above-noted Maxwell and Maxwell et al patents are incorporated in their entireties herein by reference.
Carbon dioxide and relatively high concentrations of oxygen are blood parameters which are quite difficult to measure accurately.
It clearly would be advantageous to provide blood parameter sensing systems which provide enhanced accuracy.